One part Field of the Dead, one part Life from the Loam (sort of). Two very powerful abilities.
Some of you will read the landfall ability and go the Timmy route and think Omnath, Locus of Rage and flooding the board with Zombies with ramp cards like Harrow.
Others will think of combos that you can do and go the Jonny route. Think The Gitrog Monster.
Others will take this even further and add some Spike elements, think Armageddon.
Dredging
The first most important part is that his ability to dredge 2 to return a land from graveyard means that you NEVER want to draw another land the entire game. Drawing a land is almost completely wasted once you are setup with The Necrobloom.
If you are never drawing cards and only dredging then how do you do other plays? If you know anything about Magic, it's that your graveyard is a resource and if you've played or seen other constructed formats like Vintage dredge, you'll understand that cards in hand don't really matter.
One of the main goals is to keep dredging to setup an Aftermath Analyst or World Shaper to really get a foothold on bigger plays.
The idea is that you are wanting to mill your deck as there are ways to get them back from graveyard within lands themselves.
With The Necrobloom ability to return lands to your hand from graveyard you are wanting to mill these lands as well.
Mortuary Mire, Takenuma, Abandoned Mire, Volrath's Stronghold, Witch's Cottage, Shifting Woodland are lands which gives you access to creatures in your graveyard.
Note that Witch's Cottage can be searched with any of the black fetch lands, so searching for Swamp types is important during those early searches.
There are also flashback cards (and others) that can bring creatures back, so you will have a lot access to cards that you want and need via your graveyard.
As Aftermath Analyst is a key card, you'll find Sevinne's Reclamation, Dread Return, Dusk // Dawn, Genesis, Unburial Rites and Angel of Indemnity can all be cast from graveyard to get it, or other cards at the time of casting that you want.
Now with any cycling land you can keep discarding it to dredge 2 and because it's now in graveyard you can return it.
This is most likely the way you will be playing each turn unless you already have a good card in hand to cast.
Obviously the cycling cards are more mana intensive for this interaction, but there is Fluctuator or Bone Miser which allows you to actually combo by milling as much of your library as you want. Bone Miser also allows you to use Barren Moor do this and nets an additional each time.
Once you've milled a decent portion of your library probably the best example is to use Dread Return which is easily casted with your tokens and bringing back Angel of Indemnity which in turn can bring say Aftermath Analyst/World Shaper, Trove Warden.
You will bring all the land into play triggering an army of Zombies and Trove Warden will trigger putting realistically all the other 3 mana or less cards. This is where Phyrexian Tower is good in the deck for sacrificing World Shaper and Trove Warden in a timely manner.
I've stated that you don't want to be drawing cards, but with Sylvan Library you can dredge 3 times rather than take the draws (if you have 3 lands in graveyard) and you won't have any cards drawn so don't have to pay life. You will end up with 3 lands in hand, so not perfect but this card is still great to play on turn 2 to still draw some early game cards and also you can use it to stack the top of library so you can just dredge away lands and draw the nonland card you want.
Bazaar of Baghdad will mill for an additional 4 each turn and discarding the lands is perfect in the long run. It is overall card disadvantage but you are fine being empty handed.
Because you never want to be drawing a land, the deck has most of the top of library tutor effects to find good cards as well as make sure you don't have a wasted land draw.
Hall of Heliod's Generosity is another land that can put an enchantment card you might want or need, so again filling up graveyard is a resource to be plundered.
Landfall creating token creatures
When I first drafted the deck I had quite a few aristocrat cards, which is essentially sacrificing your creatures to draw cards.
I read create 0/1 tokens and I immediately think Skullclamp. However as I said drawing cards is not what you want to be doing at all.
You want cards either in your graveyard or to remain in your library for search to put directly into play.
So I ended up removing most of them. Instead the token creatures are about generating extra mana through mainly Earthcraft, Cryptolith Rite and Gaea's Cradle.
However Evolutionary Leap is the perfect way to get value out of sacrificing tokens as it ensures not drawing lands.
Wight of the Reliquary is great to get key lands into play.
Yawgmoth, Thran Physician is the only aristocrat draw card in the deck, but he has the ability to discard lands you draw or dredge so this makes him perfect as creature removal and not hindering your plan.
Perilous Forays has a loop with The Necrobloom creating a token, so for each you can keep getting lands with a basic land type. There are 14 of them in the deck, so you should be able to fetch them all out in a couple of turns as you keep putting more mana into play to activate more times. There is Earthcraft, Nissa, Resurgent Animist and Tireless Provisioner that combo to allow you do get them all at once paying for the each time.
I really like this plan because it allows you to get a massive mana base without using your graveyard against graveyard hate.
Of note when you are dredging you'll be putting a large number of these basic land types into your graveyard, so won't be searchable.
The deck has two flashback cards which allow you to shuffle cards back in with Turn the Earth and Krosan Reclamation, so often you'll want to put these lands back in. These cards are a bit of insurance against graveyard removal as well maybe putting some key cards back into deck, so that you can setup again.
Another tech card against graveyard hate is Emerald Dragon // Dissonant Wave which can cancel triggers from cards like Bojuka Bog and Relic of Progenitus.
Even though it's a landfall Commander, I haven't gone into enabling this on a larger scale. There is no land ramp outside of Aftermath Analyst/World Shaper.
For this reason I have more value creatures with landfall, as you still do guarantee double triggers with fetch lands.
Lotus Cobra, Nissa, Resurgent Animist, Tato Farmer, Tireless Provisioner, Trove Warden are the ones that fit best with this deck.
I've stayed away from usual suspects like Scute Swarm and Avenger of Zendikar simply because the 2/2 Zombie tokens are going to be enough to get the job done most games. I mean Field of the Dead is a win condition in a lot of decks and we have that from the Command zone. There is an actual Field of the Dead to double up on this.
Removal
For the reason that you are wanting to mill your deck and you have ways of getting creatures from graveyard, the removal comes in the form of creatures. Caustic Caterpillar, Haywire Mite, Selfless Glyphweaver // Deadly Vanity, Magus of the Disk.
Once you are deeper into the game, then you can just keep recurring for example Selfless Glyphweaver // Deadly Vanity to keep wiping the board combined with a Takenuma, Abandoned Mire or Volrath's Stronghold.
Combo/Value
Hermit Druid will mill a huge portion of your deck as there are only 3 basics.
The Gitrog Monster has been notoriously combined with Dakmor Salvage and an ongoing discard outlet in cEDH.
In this deck as long as you mill at least one land then you can keep going and the deck almost half lands so you have 50/50 odds at keeping the mill going. You are going to get a bunch of lands in hand realistically. When you go to discard phase you'll probably have more than 7, so you can just discard a land and dredge it back, to then discard it again, which you loop as many times as you want.
Lands
As at the heart this is a lands deck. I've mentioned most of the key lands already but there are other that give you options.
For removal there is Blast Zone, Boseiju, Who Endures.
For additional mana there is Cabal Coffers+Urborg, Tomb of Yawgmoth and Gaea's Cradle which with tokens means you can get large numbers of creatures into play.
Urza's Cave is a nice one to play each turn to get some of these key lands into play.